News Release from: Allegro MicroSystems Europe
Edited by the Electronicstalk Editorial Team on 24 November 2003
Synchronous rectification for fast load response
Two new families of synchronous-rectification step-down switching regulator control ICs provide fast load response and high efficiency in power management applications.
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Two new families of synchronous-rectification step-down switching regulator control ICs provide fast load response and high efficiency in power management applications. The new SI-8011NVS and SI-8511NVS are ideally suited to use in equipment such as laptop PCs and digital televisions, where their efficiency levels of up to 93% can provide substantial reductions in power consumption. In particular, they meet the need for larger current, more accurate power-supply voltage and higher-speed response to the sudden load dumps that can be encountered in high-speed digital processing systems.
The high efficiency of the new devices - 93% for the SI-8011NVS and 92% for the SI-8511NVS - results from the use of synchronous rectification, which provides substantial savings in energy consumption over the conventional asynchronous method.
In addition, they offer a very short load response time of 20us by using Sanken's proprietary self-oscillation method known as pulse ratio control.
Oscillation frequency is 250kHz for the SI-8011NVS and 400kHz for the SI-8511NVS.
In the Sanken synchronous switching regulation technique, N-channel mosfets are used instead of the external discrete diodes in conventional switching regulator circuits, which introduce dropout voltage and hence limit the efficiency.
In particular, the new technique offers dramatic efficiency improvements at high output current levels.
Pulse ratio control is a self-oscillation technique in which the on and off time are controlled simultaneously.
Not only does it provide fast load response: it also allows the use of capacitors with low equivalent series resistance, with resulting economies in design.
The regulators provide a highly stable reference voltage of 1.1V +/-1.2%.
The output voltage can be set from 1.1 to 6V by using two external resistors, while the output current can be set at up to 10A by changing the external power mosfets at the output stage.
The operating frequency can also be varied with external resistors: from 150 to 250kHz for the SI-8011NVS and from 240 to 400kHz for the SI-8511NVS.
These high frequencies allow the use of compact choke coils.
Both device families feature built-in overcurrent protection, and the SI-8511NVS also offers overvoltage protection.
Other features include soft-start output on/off control and a pin for monitoring output voltage status.
The new regulators are supplied in compact low-profile (7.9 x 7.6 x 1.5mm) surface-mount SSOP-24 packages.
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